Fig. 1.

A, In vitroskin-nerve preparation. B, Electrical stimulation procedure used to “mark” C fibers. C fibers have a stable latency after supramaximal electrical stimulation (3 sec interstimulus interval) of the receptive field (traces 1–2). However, after adequate activation of the fiber with a mechanical stimulus (trace 3, mech. stim.), there is a typical shift in the latency of the electrically evoked response that recovers gradually (traces 4–7). The shift in latency and recovery indicates that both the electrically and the mechanically evoked action potentials were evoked from the same unit.